The promoter of the araBAD operon from E. coli is activated in the presence of arabinose and the absence of glucose and directs expression of genes encoding enzymes required for arabinose metabolism. 

Unlike the cases of lac and gal genes, where a repressor and an activator work together, here two activators work together: AraC and CAP. 

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#Unit 10. Ecological Principles

Species turnover on islands is generally low - The number of species on an island might remain the same, but the composition of the species should change continuously as new species colonize the island and others become extinct.

TLS Online TPP Program

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#Unit 10. Ecological Principles

Sum total of all the variety of living organisms on earth constitute biodiversity.

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#Unit 10. Ecological Principles

 The most important of them are 

Genetic Diversity

Species Diversity 

Ecological diversity

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#Unit 10. Ecological Principles

Genetic diversity: It refers to the variety of genes contained within species of plants, animals and micro-organisms. If a species has more genetic variation, it can adapt better to the changed environmental conditions. 

TLS Online TPP Program

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#Unit 10. Ecological Principles

Diversity within species 

450-700 (mycoplasma)

4000 in bacteria (eg. Escherichia coli)

13,000 in Fruit-fly (Drosophila melanogaster)

32,000 – 50,000 in rice (Oryza sativa)

35,000 to 45,000 in human beings (Homo sapiens sapiens). 

TLS Online TPP Program

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#Unit 10. Ecological Principles

Species diversity - Number of species

Western Ghats have greater amphibian species diversity than the Eastern Ghats. 

The overall richness of species is concentrated in equatorial regions and tends to decrease as one moves from equatorial to polar regions.India has 390 different mammals (rated eight highest in the world); 1,232 species of birds (eighth in the world); 456 species of reptiles (fifth in the world) and 45,000 plant species, of which most are angiosperms, (fifteenth in the world)